2006-2009 Honda S2000 Differential Carrier: Decoding Whines, Clunks, and AP2 Strength

Key Differences: 2006-2009 (AP2) vs. Earlier Models

While the carrier assembly fits all 2000-2009 Honda S2000 models, the units found in 2006-2009 vehicles are a later AP2 revision and are considered more robust than the earlier AP1 (2000-2005) versions. The differential housing is slightly stronger, but the most significant difference for installation is the propeller shaft (driveshaft) connection. AP2 models use different mounting bolts than AP1 models.

Symptoms of a Failing Carrier Assembly

Differential problems can manifest as distinct noises and vibrations. Paying attention to when and how they occur can help you pinpoint the issue.

Noises

• Whining or Howling: A high-pitched whine that changes with vehicle speed is the most common symptom of worn ring and pinion gears. The noise may be most noticeable during steady-speed cruising, acceleration, or deceleration. In an S2000, some minor gear whine can be normal, but a loud or changing whine indicates a problem.
• Clunking or Banging: A loud clunk when shifting, especially into first gear or reverse, or when getting on and off the throttle, points to excessive backlash (play) in the gears or worn differential mounts.
• Grinding or Clicking: A grinding or clicking sound, particularly when making tight turns from a stop, can mean the internal spider gears or the limited-slip unit itself is damaged. This can sometimes be confused with bad CV joints on the axles, so further diagnosis is needed.

Vibrations

A vibration that you can feel through the floor or seat, which increases with speed, can be caused by worn bearings or an imbalanced component within the differential. However, these vibrations are very often caused by failed differential mounts, which are a common issue on the S2000.

Known Issues, TSBs, and Recalls

The S2000 differential is known to be a weak point, especially on cars that are driven hard or have increased power. The primary design flaw is not necessarily weak gears, but bearing caps that can shift or 'walk' under heavy load. This movement allows the gear mesh to become misaligned, which quickly leads to catastrophic failure of the ring and pinion gears.

• Technical Service Bulletins (TSBs): While there are no major recalls for the 2006-2009 differential, Honda has issued TSBs in the past regarding the correct type of differential fluid to use. TSB #02063 was also issued for a 'Rear Vibration During Acceleration' on earlier models, which can be related to driveline issues.
• Recalls: There are no specific recalls for the differential carrier assembly on 2006-2009 Honda S2000s.

Step-by-Step Diagnosis

If you suspect your differential is failing, a fluid check is the best place to start.

1. Lift the car: The car must be perfectly level to get an accurate fluid level reading and to ensure it drains completely. Use four jack stands on a level surface.
2. Locate the plugs: The differential has two plugs: a fill plug (23mm) on the upper rear cover and a drain plug (24mm) on the bottom.
3. Always open the fill plug first: This ensures you won't be stuck with an empty differential if the fill plug is seized.
4. Drain the fluid: Place a drain pan underneath and remove the 24mm drain plug. Let the fluid drain completely.
5. Inspect the drain plug: The drain plug is magnetic. It is normal to find a small amount of fine, metallic paste or sludge on it. This is normal wear. However, if you find large metal flakes or chunks of metal, it is a clear sign of severe internal damage.
6. Refill with proper fluid: Reinstall the drain plug with a new washer and torque it to 33 ft-lbs. Fill the differential through the fill hole until fluid begins to seep out. The capacity is approximately 0.81 quarts. Many owners recommend using a high-quality synthetic 75W-110 or 75W-140 gear oil for better protection than the original fluid specified.

Buying a Used 2006-2009 Carrier Assembly

Given that a new OEM carrier assembly is prohibitively expensive (often over $4,000) and may be discontinued, a quality used OEM unit is the most practical choice for most owners. Aftermarket options are typically geared towards racing and can be noisy and expensive.

• Mileage vs. Condition: Mileage is less important than how the car was treated. A low-mileage differential from a car that was frequently launched or tracked could be in worse shape than a higher-mileage unit from a car that was driven gently. The fluid inspection is your best guide to its internal condition.
• Physical Inspection: Before buying, ask the seller to drain the fluid and provide a clear picture of the magnetic drain plug. Any large metal chunks are a major red flag. Inspect the housing for any cracks, especially around the mounting points. Check that the input and output flanges spin smoothly by hand with no grinding or excessive play.
• Verify the Part: Ensure you are buying a complete carrier assembly. Look for part numbers like 41200-PCZ-023, 41200-PCZ-A01, or 41200-PCZ-A51 to help identify it as a later AP2 unit.
• Why Used OEM is Better: A used OEM differential maintains the quiet operation and smooth engagement intended for a street car. It is a direct-fit, proven component. The cost savings are significant, with used units often selling for a fraction of the new price.

Rebuild vs. Replace

Rebuilding an S2000 differential is a complex job that requires special tools and expertise to properly set the pinion depth, bearing preload, and ring gear backlash. An incorrect setup will lead to immediate noise and rapid failure. For most DIY mechanics and even many professional shops, replacing the entire carrier assembly with a known-good used unit is faster, more reliable, and often more cost-effective than attempting a rebuild.

Cost to Replace a Honda S2000 Carrier Assembly

Related Parts to Replace at the Same Time

When replacing the differential, it is highly recommended to inspect and likely replace the differential mounts. The original mounts are fluid-filled and prone to tearing, which causes severe driveline clunks and vibrations. Upgraded polyurethane or solid mounts are a popular choice. Also plan on using new crush washers for the fill and drain plugs and consider replacing the axle seals and propeller shaft bolts.

Key Installation Torque Specs